sipr: fix get_bits(0) calls

Zero-length get_bits() is undefined, must check before calling.
Signed-off-by: Mans Rullgard <mans@mansr.com>

libavcodec/sipr.c

@@ -194,14 +194,16 @@ static void decode_parameters(SiprParameters* parms, GetBitContext *pgb,
 {
     int i, j;
 
-    parms->ma_pred_switch           = get_bits(pgb, p->ma_predictor_bits);
+    if (p->ma_predictor_bits)
+        parms->ma_pred_switch       = get_bits(pgb, p->ma_predictor_bits);
 
     for (i = 0; i < 5; i++)
         parms->vq_indexes[i]        = get_bits(pgb, p->vq_indexes_bits[i]);
 
     for (i = 0; i < p->subframe_count; i++) {
         parms->pitch_delay[i]       = get_bits(pgb, p->pitch_delay_bits[i]);
-        parms->gp_index[i]          = get_bits(pgb, p->gp_index_bits);
+        if (p->gp_index_bits)
+            parms->gp_index[i]      = get_bits(pgb, p->gp_index_bits);
 
         for (j = 0; j < p->number_of_fc_indexes; j++)
             parms->fc_indexes[i][j] = get_bits(pgb, p->fc_index_bits[j]);